The present invention relates generally to an apparatus used in the manufacture of glass optical fiber and more particularly to a cooling apparatus for cooling glass optical fiber after it is drawn from a preform but prior to coating with appropriate coating materials.
In the process for making optical fibers used in telecommunication systems and the like, the fiber is drawn from a glass preform at elevated temperatures. Thereafter, the fiber must be cooled to approximately room temperature to permit coating thereof with appropriate polymeric coating materials, such as ultraviolet (uv) cured acrylate and silicones or thermally cured silicones, to provide protection and transmission capabilities to the coated fiber.
In order to obtain fast cooling rates for the fiber draw process and thus faster draw speeds, the boundary layer of heated air, which lies very close to the surface of the hot fiber thereby preventing efficient heat transfer, must be removed. Present coolers for fibers utilize turbulent gas flow over a short length (varying from five (5) to eighteen (18) inches) of the moving fiber. The turbulent flow of gas over the fiber surface has been shown to strip off the boundary layer of heated air, thus allowing the fiber to cool more rapidly. However, the turbulent flow of gas over the fiber surfaces causes the fiber to vibrate along its length which results in unacceptable variations in the outer diameter of the optical fiber.
Two embodiments of one known cooling device are shown in U.S. Pat. No. 4,437,870. This device utilizes a flow of dry, cooled helium gas having flow components directed along and toward the moving fiber. In the second embodiment, the helium is diffused through a porous member in an attempt to minimize the vibration of the fiber.